Plastic semiconductor packages are fabricated using lead frames. A conventional lead frame comprises a stamped, or etched metal strip, adapted to support multiple dice for packaging. The lead frame supports the dice during a molding process, and provides the internal signal traces and terminal leads in the completed packages. A conventional plastic package includes a semiconductor die attached to a portion of the lead frame, and encapsulated in a plastic body.
One consideration in designing a plastic package is heat transfer from the die. Operation of the integrated circuits within the die generate heat which must be dissipated. In a conventional plastic semiconductor package, the bulk of heat transfer from the encapsulated die is through the terminal leads of the package. However, as circuit densities increase, semiconductor dice generate additional heat, and the leads of the package are not always able to efficiently dissipate the heat.
This has led to the development of semiconductor packages that include a heat sink. Typically, the heat sink comprises a metal plate embedded in the plastic body of the package. Representative heat sink packages are described in U.S. Pat. No. 5,666,003 entitled "Packaged Semiconductor Device Incorporating Heat Sink Plate", and in U.S. Pat. No. 5,629,561 entitled "Semiconductor Package With Integral Heat Dissipator".
One aspect of packages that incorporate a heat sink is that the heat sink is typically an additional component. Accordingly, the heat sink must be incorporated into the package design, and tends to complicate the package fabrication process. Also, the heat sink typically only performs a heat transfer function.
It would be advantageous for a heat sink to perform other functions in the package, such as electrical and structural functions. In addition, it would be advantageous for a fabrication process to incorporate heat sinks into packages without requiring additional complicated steps. The present invention is directed to a package that includes a heat sink element that performs electrical and structural functions. In addition the present invention is directed to a simple fabrication process for forming a heat sink semiconductor package.